Information Technology Reference
In-Depth Information
Fast transport
■
High reliability
■
Redundancy
■
Fault tolerance
■
Low latency and good manageability
■
Avoidance of CPU-intensive packet manipulation c aused by sec urit y, inspection,
quality of service (QoS) classification, or other processes
■
Limited and consistent diameter
■
QoS
■
When a network uses routers, the number of router hops from edge to edge is called the
diameter. As noted, it is considered good practice to design for a consistent diameter
within a hierarchical network. The trip from any end station to another end station across
the backbone should have the same number of hops. The distance from any end station to
a server on the backbone should also be consistent.
Limiting the internetwork's diameter provides predictable performance and ease of trou-
bleshooting. You can add distribution layer routers and client LANs to the hierarchical
model without increasing the core layer's diameter. Use of a block implementation isolates
existing end stations from most effects of network growth.
Distribution Layer
The network's distribution layer is the isolation point between the network's access and
core layers. The distribution layer can have many roles, including implementing the follow-
ing functions:
Policy-based connectivity (for example, ensuring that traffic sent from a particular
network is forwarded out one interface while all other traffic is forwarded out another
interface)
■
Redundancy and load balancing
■
Aggregation of LAN wiring closets
■
Aggregation of WAN connections
■
QoS
■
Security filtering
■
Address or area aggregation or summarization
■
Departmental or workgroup access
■
Broadcast or multicast domain definition
■
Routing between virtual LANs (VLAN)
■
Media translations (for example, between Ethernet and Token Ring)
■